A plasma processing apparatus has a processing chamber to contain one or more substrates such as semiconductor substrates, and during plasma processing of the substrate or substrates, nonvolatile reaction products occur and deposit on an inner wall and the like of the processing chamber. In the subsequent processing, the deposit may separate from the inner wall and the like of the processing chamber and may fall and deposit as dust particles on substrate surface or surfaces under processing. It is to be noted that in the background art to be described hereinafter, the processing chamber will be assumed to contain a plurality of substrates at the same time.
The deposited dust particles cause short-circuiting, breakage and/or incomplete etching of interconnecting electrical conductors of integrated circuits arranged on the substrate surfaces, and hence, become a cause of unacceptable semiconductor devices. Such dust particles, therefore, lead to a reduction in yield in the fabrication of semiconductor devices. To avoid this problem, the processing chamber is opened to the atmosphere, and components in the processing chamber are replaced by swap components which have been cleaned up beforehand, or as an alternative, the processing chamber is subjected to so-called wet cleaning that the inside of the processing chamber is wiped off with pure water or alcohol to clean it up.
The conditions of the inner wall of the processing chamber shortly after the wet cleaning are different from the corresponding conditions during steady mass fabrication. Accordingly, the processing performance of the plasma etching apparatus shortly after the wet cleaning, such as etch rate, etch rate distribution in each substrate surface, etch selectivity (etch rate ratio) between a material under etching on each substrate and its corresponding mask or underlying layer, etched profiles, is different from that of the same plasma etching apparatus during steady mass fabrication.
For the prevention of occurrence of such a problem, it is a common practice to perform processing called “seasoning discharge” (which may hereinafter be called simply “seasoning”) such that the conditions in the processing chamber, which have been changed by wet cleaning, are brought back close to those during steady mass fabrication. This seasoning is often performed by simulating processing of semiconductor substrates. The processing time for the seasoning is needed to be as much as that required for the processing of one to several lots (25 substrates per lot) depending upon the extent of the wet cleaning, and may widely scatter in many instances.
When the processing time required for seasoning becomes as long as the order of lots as mentioned above, a substantial number of substrates (dummy wafers) are processed during the seasoning. The processing of such many dummy wafers leads to an increase in the non-operation time of the apparatus, and hence, to a rise in the fabrication cost of semiconductor devices.
As a technology for resolving such a problem, JP-A-2004-235349 is known. This document discloses to determine the conditions in a processing chamber by calculating differences between scores of a principal component, which have been obtained by subjecting the plasma emission data of a lot (hereinafter called “the current lot”) to a principal component analysis, and scores of the same principal component in the preceding lot, determining an average of the differences in the current lot, the maximum and minimum values among the scores of the principal component in the current lot, and a standard deviation of the scores of the principal component in the current lot, and then comparing these values with preset standard deviations, respectively.
According to the above-described method of the conventional technology, however, data conditions for use in the determination of the end of seasoning have to be set newly depending upon the processing conditions for substrates, thereby making it difficult to apply the above-described method. Moreover, it may be difficult to determine the end depending upon the extent of the wet cleaning or the conditions of seasoning.